
(1) Our methods applied are
DFT with B3LYP exchange-correlation functional [1]} (DFT-B3LYP),
CCSD(T) [2]},
and FNDMC [3]} with trial wavefunctions generated from DFT-B3LYP.
Within the framework of DFT, DFT-B3LYP is a standard method
for covalent systems. Within the correlated methods,
CCSD(T) is known to be the “gold standard” in quantum chemistry.
A variety of methods and basis sets were chosen
in line with the previous results [4]} indicating
dependence of the Si-O-Si bond description on such choice.
FNDMC is known to be comparable with CCSD(T);
however, for the first time,
we applied FNDMC to an evaluation of \(\Delta E_{\rm {barrier}}\) .
